title: Genetic, biochemical, and physiological characterization of spinosad resistance in Plutella xylostella (Lepidoptera: Plutellidae).
abstract: Bioassays (at generation G2) with a newly collected field population (designated MN) of Plutella xylostella (L.) (Lepidoptera: Plutellidae) from Multan, Pakistan, indicated resistance to spinosad, indoxacarb, deltamethrin, abamectin, and acetamiprid. At G2 the field-derived population was divided into two subpopulations, one was selected (G2 to G11) with spinosad (Spino-SEL), whereas the second was left unselected (UNSEL). A significant reduction in the resistance ratio for each compound was observed in UNSEL at G12, indicating that the observed resistance to each insecticide was unstable. For Spino-SEL, bioassays at G12 found that selection with spinosad gave a resistance ratio of 283 compared with MN at G2. The resistance to indoxacarb and acetamiprid in the Spino-SEL population increased to 13- and 67-fold, respectively, compared with MN at G2. The toxicity of deltamethrin to Spino-SEL was similar to its toxicity to the MN population at G2. This suggests that spinosad selection maintained the otherwise unstable resistance to the compound. In contrast, resistance to abamectin decreased significantly from G2 to G12 in Spino-SEL. Logit regression analysis of F1 reciprocal crosses between Spino-SEL and the susceptible Lab-UK indicated that resistance to spinosad was inherited as an autosomal, incompletely recessive trait. The spinosad resistance allele significantly delays the developmental time, reduced pupal weight, number of eggs laid, and number of eggs hatched compared with Lab-UK. Further analysis suggests Spino-SEL exhibited a significantly lower intrinsic rate of population increase (r(m)) to all other populations tested.
authors.affiliation: Department of Biochemistry, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom. h.a.sayyed@sussex.ac.uk
authors.forename: Ali H
authors.initials: AH
authors.lastname: Sayyed
authors.forename: Shafqat
authors.initials: S
authors.lastname: Saeed
authors.forename: M
authors.initials: M
authors.lastname: Noor-Ul-Ane
authors.forename: Neil
authors.initials: N
authors.lastname: Crickmore
mesh_terms: D000818:Animals; D003433:Crosses, Genetic; D004338:Drug Combinations; D007305:Insecticide Resistance / Q000235:genetics / Q000502:physiology; D007306:Insecticides / Q000494:pharmacology*; D018942:Macrolides / Q000494:pharmacology*; D009036:Moths / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D010063:Ovum / Q000187:drug effects / Q000502:physiology; D010154:Pakistan; D011679:Pupa / Q000187:drug effects / Q000235:genetics / Q000502:physiology
chemical_list: D004338:Drug Combinations; D007306:Insecticides; D018942:Macrolides; C415329:spinosad